Para-magnetic hard alloys

ABSTRACT

Para-magnetic WC base hard alloys comprising a carbide composition primarily consisting of tungsten carbide and a binder consisting of nickel and molybdenum wherein a part of said nickel is replaced by an eutectic Ni-P composition.

EJIIEIM SIaies Patent [191 Miyashita et a1. May 22, 1973 [5 1PARA-MAGNETIC HARD ALLOYS References Cit d [76] Inventors: HirotoahiMiyashita, 4724 Ozasa UNITED STATES PATENTS Danchl; Tomio Nishimura, 225Gaza Notame; Sumiharu Tom, 2,711,009 6/1955 Redmond et a1. ..75 203 8020m Shimay FOREIGN PATENTS OR APPLICATIONS kuoka, Japan 217,445 10/1957Australia ..75/203 [22] Flledz Sept. 10, 1971 211 App]. No: 179 496Primary Examiner-Benjamin R. Padgett Assistant Examiner-B. HuntAtt0rneyLinton & Linton {52] [1.8. CI. ..29/182.7, 29/182.8, 75/203,

[57] ABSTRACT PARA-MAGNETIC HARD ALLOYS The present invention relates topara-magnetic hard alloys having a high toughness suitable formanufacture of dies, heat resistant material and structural members,especially clocks or watches in the field for which nonmagnetism isrequired.

Hard alloys are generally prepared by the sintering process of carbideof metals included in IV, V and VI Groups in the periodic table,especially tungsten carbide with an iron group metal as a binder,generally cobalt, and they are used in a wide variety of applicationssuch as cutting tools, dies or heat resisting materials. All of the irongroup metals, i.e. iron, cobalt and nickel, used as a binder metal,however, are ferro-magnetic elements, and therefore, the hard alloysprepared with these binder metals are ferro-magnetic ones.

It is known that a para-magnetic tungsten-carbidenickel alloy may beprepared by limiting the carbon content of the tungsten carbide to 5.95percent by weight on the basis of tungsten carbide, but a decrease ofthe carbon content deteriorates the toughness of the alloy due to thegeneration of a double carbide.

We improved the above-mentioned difficulty by an invention whereinnickel and molybdenum are used as a binder composition for a carbidecomposition primarily consisting of tungsten carbide, and a part of saidnickel is replaced by an eutectic Ni-P composition, or a part of saidtungsten carbide particles are previously coated with the Ni-Pcomposition by the electroless plating. The resulting mixture is thensintered. We found that during said sintering process the molybdenum isdissolved in the nickel, rendering the metallic binder phasepara-magnetic, thus obtaining a novel hard alloy of a high toughnesswith a carbon content without generating free carbon or a doublecarbide.

The present invention is based on the abovementioned founding.

The para-magnetic hard alloys of the present invention may be producedby the sintering process of mixed particles consisting of 70-99 percentby weight of a carbide composition primarily comprising tungsten carbidewith or without one or more members selected from a group consisting oftantalum carbide, titanium carbide, niobium carbide, vanadium carbide,chromium carbide, zirconium carbide and hafnium carbide and l-30 percentby weight of the binder composition comprising 2-30 percent by weight ofa Ni-P composition containing 8-l4 percent by weight of phosphorus, -50percent by weight of molybdenum and nickel constituting the remainder.Alternatively, the mixed particles may contain the carbide particlespreviously coated with the Ni-P composition by the electroless plating.

The reason for restricting the content of the carbide composition to70-99 percent by weight is based on the fact that lesser content than 70percent by weight substantially decreases the hardness of the produceand larger content than 99 percent by weight deteriorates the toughnessto an impractical extent.

The other carbides such as tantalum carbide, titanium carbide, niobiumcarbide, vanadium carbide, chromium carbide, zirconium carbide orhafnium carbide may be added as a simple substance as the conven tionalmanner, or may be added after the production of a double carbide withthe tungsten carbide. When two or more kinds of different carbides areto be added, they may be in a form of a solid solution carbide.

Nickel is used as the binder metal for the reasons that it produces analloy having the substantial same physical properties as that of acobalt bonded alloy or cemented carbide, and that the Curie point ofnickel is the lowest out of the iron group metals.

A part of the molybdenum is converted into a carbide form during thesintering process, but it may be used for the reason that when dissolvedin nickel in an amount more than 9 percent by weight, molybdenum impartsa para-magnetism at the room temperature.

The reason for restricting the added amount of molybdenum in the bindercomposition to 15-50 percent by weight is based on the facts that withthe amount less than l5 percent by weight, the molybdenum content in thebinder phase decreases less than 9 percent by weight producing theferro-magnetism, and with the content over 50 percent by weight, thehardness of an alloy deteriorates substantially.

Further, the reason for the step in which a part of nickel particles isreplaced by the eutectic Ni-P composition containing 8-14 percent byweight of nickel, and then the total nickel is added to control thecarbide formation of molybdenum by reducing the eutectic temperature ofthe sintered product and to render the binder composition para-magneticby increasing the molybdenum content in the binder phase. Also, when apart of the carbide particles previously coated with the Ni-Pcomposition containing 8-14 percent by weight of nickel by theelectroless plating is used, the carbide formation of molybdenum isfurther prevented to improve the effect to increase the molybdenumcontent in the binder phase.

As mentioned above, it is possible to prepare novel paramagnetic WC basehard alloys having a hightoughness by the addition of the bindercomprising nickel, molybdenum and the eutectic Ni-P composition.

The present invention will be further described by way of the followingExamples.

EXAMPLE 1 Particle mixture comprising 81 percent by weight of tungstencarbide having a grain size of 1.4 microns, 1 percent of which beingcoated with NiP powders con taining 10 percent by weight of phosphorusby the electroless plating, 7 percent by weight of molybdenum having agrain size of 1.2 microns and 12 percent by weight of nickel having agrain size of L3 microns is thoroughly mixed in a solvent of acetonewith a ball mill for 72 hours. After the mixing, the mixture ispressmolded and vacuum sintered for 1 hour at the temperature of l,300 Cunder the similar steps for the convert tional hard alloys to produce apara-magnetic hard alloy in accordance with the present invention.

The resulting alloy exhibits the para-magnetism, in other words themagnetic saturation is zero.

The Curie point exhibiting the term-magnetism are obtained at 127 K (146C) as shown in the accompanying graph of reciprocal susceptibility v.absolute temperature. The product shows the hardness of HRA 906 and thetransverse rupture strength of 150. Kg/sq.

EXAMPLE 2 An alloy prepared in the same vacuum sintering process as inExample 1 from a particle mixture comprising 73 percent by weight oftungsten carbide having a grain size of 1.5 microns, 15 percent byweight of nickel having a grain size of 1.3 microns, 10 percent byweight of molybdenum having a grain size of 1.2 microns and 2 percent byweight of Ni-P composition containing 1 1 percent by weight ofphosphorus shows the para-magnetism at the room temperature, a hardnessof HRA 88.6 and a transverse rupture strength of 168 Kg/sq. mm.

We claim:

1. Para-magnetic WC base hard alloy prepared bv the sintering processfrom a particle mixture comprising l-3O percent of a nickel base bindercomposition conbide. zirconium carbide and hafnium carbide.

1L 2 x x t

2. A para-magnetic WC base hard alloy as claimed in claim 1 including atleast one member selected from a group consisting of tantalum carbide,titanium carbide, niobium carbide, vanadium carbide, chromium carbide,zirconium carbide and hafnium carbide.